The present invention relates to a charge air cooler for a supercharged combustion engine, and particularly to control over the flow of air to be cooled through the air cooler.
The amount of air which can be supplied to a supercharged combustion engine of a vehicle depends on the pressure of the air but also on the temperature of the air. Supplying the largest possible amount of air to a supercharged combustion engine entails cooling compressed air in a charge air cooler before it is led to the combustion engine. The charge air cooler is usually situated in front of the conventional radiator of a vehicle. A charge air cooler usually comprises two tanks and a plurality of tubular elements arranged in parallel which connect the tanks to one another. The parallel tubular elements are arranged at a distance from one another so that surrounding cold air can flow between the tubular elements and cool the compressed air in the tubular elements. Depending on the efficiency of the charge air cooler, the compressed air can be cooled to a temperature more or less corresponding to the temperature of the surrounding air.
Charge air coolers in vehicles are usually so dimensioned as to be of relatively good efficiency. In certain circumstances when there is a cold ambient temperature and/or very high air humidity, the compressed air in a charge air cooler is cooled to a temperature below the dewpoint temperature of the air. Water vapour in the compressed air condenses, with the result that water in liquid form is precipitated in the charge air cooler. When the temperature of the surrounding air is very low, there is also risk that water in liquid form may freeze to become ice inside the charge air cooler. This may cause operational malfunctions if the cooler freezes up, resulting in a lack of air supply to the combustion engine. When a vehicle is started up from cold, it is also advantageous that the cooling of the compressed air led to the supercharged combustion engine should at first be reduced to enable the combustion engine initially to produce hotter exhaust gases which will warm up the vehicle's catalyst quicker. GB 1 255 956 refers to a charge air cooler for cooling compressed air before it is led to a combustion engine. The charge air cooler comprises a bypass line with an adjustable valve so that at least a desired portion of the compressed air can be led past the charge air cooler without being cooled. The uncooled portion and the cooled portion of the compressed air are thereafter mixed before being led to the combustion engine. Cooling a suitable portion of the compressed air makes it possible for the temperature of the air led to the combustion engine to be controlled to a desired value.